12z guidance depicts no major changes in expected weather trends across the area. The next round of cold air is just now entering the extreme northwest counties of our cwa, and will attempt to undercut the bands of rain that continue to develop near the Kansas/OK border and advected east-northeast into the mid-Mississippi Valley.

The cold air will become deep enough to begin a transition of the rain to sleet and perhaps freezing rain as the night progresses, but as the cold air becomes deep enough to create a mix from central MO into central Illinois it appears that the precipitation will be winding down. However, it should be a different story a bit further south late tonight and into Wednesday morning, where the precipitation will be more sustained as the cold air reaches critical depths. Overall, the general trend overnight across the southeast half of the County Warning Area should be for the rain to first become mixed with sleet and freezing rain as the night progresses. The continued southward progression of the cold air will then change this icy mix over to all snow near the I-44 corridor early Wednesday, with the precip in our far southern counties changing over to all snow no later than midday, and then winding down Wednesday evening.

The precipitation late tonight and into Wednesday has a lot going for it. This mornings upper air data indicated 10c 850mb dewpoints already into SW MO, and this moisture will increase into Wednesday as the SW low level flow just above the cold air continues the moisture transport. Lift generated by already strong isentropic ascent will be increasing as baroclinicity strengthens to our south, with the southwest flow aloft ejecting several shortwaves into the mid Mississippi Valley enhancing the deep lift further. Believe the intensity of the lift is showing up in most of the synoptic models as they all have some indication of the upper level jet over the upper Great Lakes backbuilding into our area with time.

Quantitative precipitation forecast and thermal profiles suggest heavy wintry precipitation is likely from Arkansas into southern MO and southern Illinois. Snowfall generated from these parameters indicate 4 to 6 inches of snow/sleet can be expected over our far southern counties, and because of this snowfall along with the light glazing produced by the freezing rain will be going out with a Winter Storm Warning for late tonight into Wednesday evening for areas along and south of a Centerville...Sparta line. Just north of the warning area will be a Winter Weather Advisory from the Eastern Ozarks into southern Illinois, for lesser snowfalls of 2 to 4 inches along with a possible glaze of ice.

It should be noted that there will be an extremely tight gradient on the northern edges of the snowfall...roughtly from near Jefferson City...through St. Louis...to around Vandalia Illinois. If the system shifts slightly north the advisory may need to be expanded into these areas...this evenings and overnight shifts will be monitoring upstream radar trends to fine tune this tight snowfall gradient.

As upper level long wave trof pushes east, the Arctic air that enters the region overnight tonight will continue to build and strengthen over the mid Mississippi Valley. Although the high will mean few clouds and dry weather, temperatures of this airmass will be extremely cold for early March. Currently, we are looking for Thursday morning lows somewhere in the 5 to 12 above range, with highs only rebounding into the 20s during the afternoon even with what should be strong sunshine.

Unseasonably cold temperatures will linger on Thursday night, but return flow should mean the beginnings of a welcomed warmup by Friday.

A split flow regime will initially be in place at the start of the extended range period featuring a broad longwave trof centered across eastern noam and a quasi Rex block along the West Coast. The Block will break down by early next week and the overall strength of the trof weakens, however we largely maintain northwest flow aloft into Monday. There will be several notable disturbances embedded within the flow aloft which will traverse the region, bringing a cold front through the area on Saturday afternoon/night and then again on Sunday night. Present indications are that cooling associated with these fronts will be weak and short-lived. In general the weekend will be characterized by near average temperatures and benign/tranquil weather conditions. Next week will feature a pronounced pattern change, rising heights aloft and above average temperatures for much of the week.

MVFR ceilings will last through much of the night at all taf sites as cold front pushes through and stratus deck remains. KUIN and kcou will likely be VFR by 10-13z Wednesday, then VFR ceilings reach kstl taf sites by around 16z. Will have to watch radar and surface reports carefully this evening as there is some chance that precip aloft now seen on regional radars may reach the surface at kstl area taf sites. For now, it appears a dry layer at 6k to 8k feet may keep this from happening so have left tafs dry. Northwest winds behind the front will become gusty and last into Wednesday.

Specifics for kstl: MVFR ceilings expected until 16z. Cold front should reach taf site by around 06z, and north winds behind the cold front will increase to around 14 knots and become gusty. Have kept taf dry for now, but will have to watch surface reports to see if precip aloft now seen on radar begins reaching the ground this evening. Expect dry air aloft to keep most precip just to the south of kstl on Wednesday, but it is a close call.